Isochaihulactone-induced DDIT3 causes ER stress-PERK independent apoptosis in glioblastoma multiforme cells.

Sheng-Feng Tsai,Horng-Jyh Harn,Michael Tao,Li-Ing Ho,Shinn-Zong Lin,Tzyy-Wen Chiou,Hong-Lin Su

doi:10.18632/oncotarget.13266

Abstract

The endoplasmic reticulum (ER) is a major site of cellular homeostasis regulation. Under the ER stress condition, Glioblastoma multiform (GBM) cells activate the unfolded protein response. In this study, we discovered isochaihulactone, a natural compound extracted from the Chinese traditional herb Nan-Chai-Hu, which can disrupt ER homeostasis in GBM cell lines. It can induce DNA damage inducible transcript 3 (DDIT3) expression which is independent of 78 kDa glucose-regulated protein (GRP78) and protein kinase RNA-like endoplasmic reticulum kinase (PERK) expression. Flow cytometry results revealed that isochaihulactone trigger the cell cycle arrest at G2/M phase and apoptosis in GBM cells. Isochaihulactone induced DDIT3 led to the expression of NAG-1. The in vivo study showed that isochaihulactone suppressed tumor growth, and DDIT3 and Caspase3 overexpressed in the xenograft model, which is consistent with the in vitro study. Overall, the data revealed that isochaihulactone disrupted ER homeostasis in cancer cells by increasing DDIT3 and NAG-1 expression. Our finding also provides a therapeutic strategy by using isochaihulactone for GBM treatment.

Highlights

The endoplasmic reticulum takes part in several cellular functions, including protein synthesis, calcium homeostasis, and phospholipid synthesis [1]
We subsequently demonstrated that damage inducible transcript 3 (DDIT3) increased NAG-1 expression in Glioblastoma multiform (GBM) cell lines, which led to tumor cell apoptosis
We discovered that the level of the endoplasmic reticulum (ER) stress modulator GRP78 did not change following K8 treatment (Figure 1F)

Summary

Introduction

The endoplasmic reticulum takes part in several cellular functions, including protein synthesis, calcium homeostasis, and phospholipid synthesis [1]. During ER stress, increased levels of unfolded proteins accumulate and cause protein kinase RNA-like endoplasmic reticulum kinase (PERK), an ER stress sensor, to activate. The other ER stress sensor, inositol-requiring enzyme 1α (IRE1α), activates the translation of HSP90 chaperone family member GRP78. GRP78 is involved in the subsequent folding steps for a subset of ER client proteins, a process called the unfolded protein response (UPR) [3]. ER stress may restore homeostasis and render the adjacent environment hospitable for tumor survival and growth [4]. The UPR is usually inactive in normal cells, but is widely overexpressed in many cancers, including breast cancer [6], leukemia [7], colon cancer [8], and brain cancer

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